Sunder Raj, a senior local police official, said that 10 security people had been wounded.

The officers were surrounded in the ambush, which took place in Dhodai, 300km south of the state capital Raipur, and they fought back in a gun battle that lasted three hours, Niwas said.

The Maoists, who killed 76 policemen in a similar assault in Chhattisgarh in April, numbered as many as 100 and opened fire with automatic weapons from a hilltop.

Major offensive

The government launched a major offensive last year to tackle the worsening uprising.

in depth

  India's costly war against Maoists
  India's battle against the Maoists
  Q&A: The Maoists of India
  Indian villagers take on Maoists
  Timeline: Major Maoist attacks

Maoist rebel groups have fought for decades throughout east and central India against state and government rule, drawing support from landless tribal groups and farmers left behind by the country's economic development.

Last month, 146 people were killed when a Mumbai-bound passenger train from Kolkata was derailed by suspected Moaists in a remote part of West Bengal state.

In another attack, a bus hit a landmine in Chhattisgarh killing 24 civilians and 11 police personnel, while 25 officers were when Maoists overran a security camp in West Bengal state in February.

The scale of recent rebel strikes has highlighted the government's struggle to find an effective strategy against the Maoists, with ministers coming under severe pressure to clamp down on the violence.

As the attacks have worsened, calls have grown for the army and air force to be drafted in.

But until now, the government has insisted that paramilitary and state police forces were capable of tackling the Maoists in their jungle bases.

Clash of views

Analysts say the government is hamstrung by internal disagreement, with some urging a more aggressive policy and others favouring a long-term strategy to addresses the plight of impoverished tribesmen and farmers.

"There is a conflict between the so-called hawks who want to crush the rebels and the so-called doves who call for development in Maoist-dominated areas to wean away their support," Ajai Sahani, a counter-terrorism expert, told the AFP news agency.

Military chiefs have made it clear that they are opposed to involving the armed forces in any direct combat operations.

Little is known about the Maoists' structure, but their current strength is estimated at between 10,000-20,000 fighters, who operate out of jungle camps where they are believed to undergo weapons and ideological training.